a designer can consider the fineness ratio, which is the length of the aircraft divided by its diameter at the widest point (L/D). It is mostly kept 6:1 for subsonic flows. Increase in length increases Reynolds number. With Reynolds no. in the denominator for skin friction coefficient's relation, as its value is increased (in laminar range), total friction drag is reduced.
The higher fineness ratio gives a longer flowpath, slowing the air more (=higher Reynolds). A slower boundary layer creates less friction downstream.
But increasing the fineness ratio increases the total surface area as well. And that is a recipe for increased friction. From the Wikipedia article on fineness ratio:
As the name implies, this is drag caused by the interaction of the airflow with the aircraft's skin. To minimize this drag, the aircraft should be designed to minimize the exposed skin area, or "wetted surface"
So, what am I missing?